This invention relates to earth boring by the rotary system and more particularly to a length of drill pipe having a wear sleeve thereabout in between the tool joints at the ends thereof, and to a method of attaching the wear sleeve to the drill pipe tube that extends between the tool joints.
Heretofore it has been disclosed in the aforementioned U.S. Pat. Nos.: 4,146,060-Garrett, 4,171,560-Garrett, that a one-piece homogeneously integral wear sleeve may be applied to the drill pipe tube prior to the attachment of the second tool joint to an end thereof. However, in the case of, e.g., used, drill pipe to which tool joints have already been welded, one at each end, this method is inapplicable unless a tool joint, e.g., one that is worn out, is cut off and replaced.
It is also known to split a wear sleeve prior to its attachment to a drill pipe tube so that the sleeve can be attached to the drill pipe tube after both tool joints have been attached. Prior U.S. patents showing various modes of attaching split wear sleeves to the drill pipe tube are discussed in the aforementioned Garrett patents.
One problem encountered with previously known split wear sleeves has been the difficulty in aligning the two segments of the split wear sleeve.
Another problem lies in the need, when welding the segments together, to bridge the gap between the segments to prevent weld metal penetrating the annulus between sleeve and tube. Such penetration would possibly damage the tube, interfere with flow of adhesive between tube and sleeve during attachment of the sleeve to the tube, and create stress risers where the weld metal engaged the tube.
Heretofore the two segments have usually been formed from a single piece sleeve which is sawed in half, leaving two gaps each a saw width wide, some type of consumable support sleeve or liner being placed inside the sleeve prior to welding the two segments together. Also, it is known to forge the two segments and to form lip and rabbet joints at the junctions of the segments, the overlapping lips serving to keep weld metal away from the drill pipe tube. Such construction is fairly expensive and the problem of alignment of the segments remains.
Summary of the Invention: (Numbers in parentheses refer to following notes).
According to the present invention, a steel wear sleeve is machined to the desired inner and outer diameters. The sleeve is then broken apart into parts of such size that they can be placed about a drill pipe tube, e.g., two semi cylindrical halves. Steps are taken to minimize or prevent plastic deformation of the two halves, both adjacent to the breaks and overall, whereby the parts can be fitted together after being placed about a drill pipe tube and, after reintegration, will be substantially round. Preferably, substantially brittle fracture (1), (2), (3) is achieved at both breaks.
First of all, diametrically opposed longitudinal external grooves are cut in the sleeve where it is to be segmented, the grooves penetrating nearly to the inner periphery of the sleeve, e.g. greater than fifty percent of the radial thickness of the sleeve, leaving only relatively thin webs connecting the segments.
The grooves provide sleeve portions of reduced cross-section thereby reducing the hoop tension required for parting, insuring that parting takes place where desired, e.g., in planes at diametrically opposite sides of the sleeve, and that parting at the grooves occurs prior to the remainder of the sleeve being loaded in excess of yield strength which would cause overall plastic deformation of the two halves, and that any yield at the breaks will be small because the breaks will occur at low stress values corresponding to lower values of plastic yield. The grooves provide stress concentrations (4) further facilitating parting. The grooves restrain plastic deformation, (5) thereby encouraging brittle fracture. The grooves provide space between the adjacent halves of the sleeve where weld metal can be inserted to join the halves together without forming an excessively radially protuberant weld joint. By scratching the bottoms of the grooves even greater stress concentration may be achieved in materials of high tensile strength to further encourage brittle fracture and localize failure at the desired planes (6).
Secondly, preparatory to parting, the sleeve is cooled, thereby to increase its notch sensitivity (7), and increase the unit yield strength (8) which promotes brittle failure (9), (10). To the same end, martensitic steel is preferred for the material of the wear sleeve (11). The sleeve is cooled to below the ductile-brittle transition temperature (12). The transition temperature depends on the heat treatment (13) and composition (14), (15) of the particular steel (15). For 1040 steel the transition temperature (start of lower shelf level) may be from zero to minus 20 degrees Fahrenheit; for 1020 bar stock it may be from minus 150 to minus 225 degrees Fahrenheit. Nil ductility temperature (16), crack arrest, dynamic tear, and drop weight tear tests (17) may also be used as a criterion for how low to cool the sleeve. Actually, there is quite a scatter to the results of such tests (18). Furthermore, test results depend greatly on the thickness of the specimen and the length of the crack (19). For best results, tests should be made with a sample of the material to be employed for the sleeve and of the same groove length, shape, thickness and history, or in other words, a test with the actual sleeve. A preferred test would be one that determines the temperature of minimum shear fracture (20). Preferably, the sleeve is cooled to an even lower temperature, In an actual case a sleeve of 1020 bar stock was cooled in liquid nitrogen at atmospheric pressure, to a temperature, e.g., of minus 195 degrees Centrigrade, (minus 320 degrees, Fahrenheit), thereby to fully, temporarily embrittle the metal of the sleeve.
Thirdly, the sleeve is parted by impact loading, thereby to raise the ductile-brittle transition temperature (2), (6), (11) and facilitate a greater degree of brittle fracture. To this end the cold sleeve is placed over an expander (e.g., a split wedge ring having a wedge cone therein) and broken apart into segments by forcing the cone into the ring. The force could be applied gradually, as in a hydraulic press (21), but preferably is applied suddenly, e.g., with a sledge hammer, thereby to reduce the time for yielding to occur by causing achievement of fracture stress in a very short period of time. Also, because the yield strength of the sleeve is greater with respect to impact loads and with low temperature, brittle failure will occur before any yield. The sleeve will fracture along the longitudinal grooves.
The sleeve could be cooled in situ while in position about the expander, if desired.
After fracture, the segments are preferably allowed to warm, e.g., to room temperature, e.g. 20 degrees Centigrade or whatever the ambient temperature of the shop may be, or any temperature consistent with ease of handling and preferably above the embrittlement temperature.
The segments of the fractured sleeve are then placed about a drill pipe tube and, according to the preferred embodiment where substantially brittle or low yield fractures are achieved, it will be found that they fit together perfectly like the broken pieces of a china cup. This insures that the segments are properly aligned and leaves no gap between the segments for weld metal to penetrate to the pipe-sleeve annulus. It is preferred that there be no pieces broken out at the fracture edges, which might allow weld metal to penetrate to the pipe. For the the same reason, in the case of less than brittle fracture, whiskering and other distortion preventing close approach of the two segments along the parting line is to be avoided.
The segments are then welded together by depositing weld metal in the longitudinal grooves. If desired, a disposable liner may be employed inside of the sleeve during welding to hold the segments in position and protect the tube in case the thin edges of the sleeve adjacent the fracture are melted away accidentally during the welding step.
The weld integrated fractured sleeve is then secured to the drill pipe tube with adhesive cement, e.g., epoxy resin; this may, for example, be done in the manner set forth in the aforementioned Garrett patents, the disclosures of which are incorporated herein by reference, or, preferably, as set forth in the contemporaneous U.S. patent application of Gerry R. Lavendar and James Oscar Chance entitled Wear Sleeve--Drill Pipe Assembly, assigned to the same assignee as the present application, now U.S. Pat. No. 4,434,125, issued Feb. 28, 1984.
Further features of the invention and objects and advantages thereof will appear from the following description of a preferred embodiment of the invention, reference being made to the accompanying drawings.